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Surround sound formats
Below is a brief description of the main surround sound
formats you’ll find on DVDs, satellite, cable and terrestrial
broadcasts, and video cassettes.
Dolby
The Dolby technologies are explained below. See
www.dolby.com for more detailed information.
Dolby Digital
Dolby Digital is a multichannel digital audio coding system
widely used in cinemas, and in the home for DVD and digital
broadcast soundtracks. It can deliver up to six discrete audio
channels, comprising five full range channels and a special
LFE (low frequency effects) channel used mainly for deep,
rumbling sound effects; hence the term “5.1-channel” Dolby
Digital.
In addition to the format features above, Dolby Digital
decoders offer downmixing for compatibility with mono,
stereo and Dolby Pro Logic audio from a number of bit rates
and channels. Another feature, called Dialog Normalization,
attenuates programs based on the average level of dialog in
a program relative to its peak level (also known as Dialnorm)
in order to achieve uniform playback level.
Dolby Digital Surround EX
Dolby Digital Surround EX (the EX stands for EXtended) is an
extension of Dolby Digital encoding whereby a surround
back channel is matrixed into the surround left/right
channels for 6.1 channel playback. This allows for
compatibility with Dolby Digital 5.1 channel decoding, as
well as for decoding using Dolby Digital EX.
Dolby Pro Logic IIx and Dolby Surround
Dolby Pro Logic IIx is an improved version of the Dolby Pro
Logic II (and Dolby Pro Logic)
decoding
system. Using the
innovative “steering logic” circuit, this system extracts
surround sound from sources as follows:
•
Dolby Pro Logic
– 4.1 channel sound (mono surround)
from any stereo source
•
Dolby Pro Logic II
– 5.1 channel sound (stereo
surround) from any stereo source
•
Dolby Pro Logic IIx
– 6.1 or 7.1 channel sound (stereo
surround and surround back) from two channel or
5.1(and 6.1) channel sources
With two channel sources, the “.1” subwoofer channel is
generated by bass management in the receiver.
Dolby Surround is an
encoding
system which embeds
surround sound information within a stereo soundtrack,
which a Dolby Pro Logic decoder can then use for enhanced
surround listening with greater sound detail.
Dolby Digital Plus
Dolby Digital Plus is the next-generation audio technology
for all high-definition programming and media. It combines
the efficiency to meet future broadcast demands with the
power and flexibility to realize the full audio potential
expected in the upcoming high-definition era. Built on Dolby
Digital, the multi-channel audio standard for DVD and HD
broadcasts worldwide, Dolby Digital Plus was designed for
the next-generation A/V receivers but remains fully
compatible with all current A/V receivers.
Dolby Digital Plus delivers multi-channel audio programs of
up to 7.1 channels (*) and supports multiple programs in a
single encoded bitstream with the maximum bit rate
potential of up to 6 Mbps and the maximum bit rate
performance of up to 3 Mbps on HD DVD and 1.7 Mbps on
Blu-ray Disc, and it outputs Dolby Digital bitstreams for
playback on existing Dolby Digital systems. Dolby Digital
Plus can accurately reproduce the sound originally intended
by directors and producers.
It also features multi-channel sound with discrete channel
output, interactive mixing and streaming capability in
advanced systems. Supported by High-Definition Media
Interface (HDMI), a single-cable digital connection is
possible for high-definition audio and video.
Dolby TrueHD
Dolby TrueHD is the next-generation lossless encoding
technology developed for high-definition optical discs in the
upcoming era. Dolby TrueHD delivers tantalizing sound that
is bit-for-bit identical to the studio master, unlocking the true
high-definition entertainment experience on high-definition
optical discs in the next generation. When coupled with
high-definition video, Dolby TrueHD offers an unprecedented
home theater experience with stunning sound and high-
definition picture.
It supports bit rates of up to 18 Mbps and records up to 8 full-
range channels (*) individually with 24-bit/96 kHz audio. It
also features extensive metadata including dialogue
normalization and dynamic range control. Supported by
High-Definition Media Interface (HDMI), a single-cable
digital connection is possible for high-definition audio and
video.
HD DVD and Blu-ray Disc standards currently limit their
maximum number of audio channels to eight, whereas
Dolby Digital Plus and Dolby TrueHD support more than
eight audio channels.
Manufactured under license from Dolby Laboratories. “Dolby”,
“Pro Logic”, “Surround EX” and the double-D symbol are
trademarks of Dolby Laboratories.
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